The invention relates to a pointer instrument, especially for a motor vehicle, having a pointer with a pointer shaft that deflects a pointer flag and having a light source that is connected so as to rotate with the pointer, it being possible for the pointer flag to be illuminated by means of the light source.
Such a pointer instrument is nowadays widely used in motor-vehicle construction practice and is thus known. In this case, the pointer shaft is designed, for example, as a light conductor and therefore permits the indirect illumination of the pointer flag by means of a rear light source. Other embodiments are known, in which the light source is arranged at the upper end of the pointer shaft so as to be invisible to the viewer and radiates directly into the pointer flag.
The disadvantage with the two above-described embodiments of a pointer instrument is that uniform illumination of the pointer flag requires specific shaping of the cross-sectional area. In particular, the underside of the pointer flag, facing away from the viewer, is inclined with respect to the pivoting plane of the pointer flag, so that the incident light is reflected there and emerges uniformly on the upper side of the pointer flag, which faces the viewer and is essentially flat.
By contrast, freely shaped pointer flags can in principle be illuminated only when both the uniform emergence of part of the light and the conduction of a further part of the light as far as an end section of the pointer flag is ensured by multiple reflection in the interior of the pointer flag. In this case, it is virtually impossible in practice to avoid differently bright portions of the pointer flag. Similar problems also occur if, instead of an essentially flat surface of the pointer flag, profiled or contoured shapes are to be used, since this hampers the emergence of the light.
In addition, on account of the comparatively low-level illumination of a curved pointer flag, it is not possible to provide for its arrangement on the rear of a diffusely transparent covering disk which covers the display, as would be increasingly desirable because of specific requirements with regards to the design.
Close limits are therefore placed on stylistic freedom if poorer legibility and, under certain circumstances, a lower-quality appearance are not simultaneously tolerated.
The invention is based on the problem of configuring a pointer instrument of the type mentioned at the beginning in such a way that almost any desired shaping of the pointer flag is made possible without impairing the legibility as a result of differences in brightness in different subareas of the pointer flag.
According to the invention, this problem is achieved in that the contour of the light source can be shaped or is shaped essentially to correspond to at least one portion of the outside of the pointer flag.
This formation of the light source achieves a uniform emission of light which is independent of the pointer shape and, as a result, increases the legibility. The pointer flag may have any desired shape having a configuration which, in particular, is also multiply curved. For this purpose, the light source is either pre-shaped to correspond to the pointer flag or, if a flexible or resilient light source is used, can be matched to the pointer flag.
The light source could be of three-dimensional form in this case. According to an advantageous development of the invention, however, the pointer is particularly light and compact if the light source is a flat radiator having a low height. In this case, the height is of the order of magnitude of one millimeter.
To this end, an embodiment of the invention in which the light source has an electroluminescent film is particularly advantageous. As a result of the low thickness and the flexible properties of such an electroluminescent film, pointer flags of any desired shape can be illuminated without difficulty, the uniform emission of light from the light source designed in this way ensuring high operational reliability. In particular, even large-area pointer flags can be illuminated in this way, without a significant change to the pointer instrument having to be undertaken. The electroluminescent film can be arranged both on the upper side of the pointer flag, inclined toward a viewer, and on the rear of a pointer flag that is designed to be transparent for this purpose.
The light source is particularly simple to produce and has a high luminance if it advantageously has an organic LED.
The light source could have a low-polymeric organic compound. A particularly beneficial development of the invention is provided, however, if the light source has an electrically excitable, light-emitting polymer.
By this means, illumination over the whole area, especially even the edge regions of the pointer flag, can be achieved. In this case, in addition to any desired coloration, segments with different colorations can also be displayed. For this purpose, the light-emitting polymer can be excited between two electrodes, at least that electrode which is inclined toward a viewer being largely transparent. In this case, the light-emitting polymer is also suitable for illuminating the edge regions of the pointer flag, it being possible at the same time for the weight of the pointer flag to be reduced significantly.
The light source can be formed as a very flat surface light emitter. As a result, a flat pointer flag with a low weight and invisible side edges can also be implemented.
A light source having a light-emitting polymer has the particular advantages of the ability to be dimmed simply and of being operated in an uncomplicated way with a DC voltage of less than 12 V, preferably below 10 V. In addition, light-emitting polymers make it possible to achieve luminances in which the light-emitting color of the light sources can easily be detected during the day, that is to say with a high ambient brightness. Because of the high luminance, such a pointer is also suitable for black-panel combined instruments in motor vehicles.
It is also particularly beneficial in this case if the pointer flag is formed as an electrode that excites the light-emitting polymer.
A polymer with the desired property can readily be applied, in accordance with the shaping carried out, to the pointer flag, which is designed to be metallic for this purpose. To this end, the second electrode is formed to be essentially transparent and is arranged approximately parallel to the pointer flag on the upper side of the polymer layer. As a result of the omission of a second, separate electrode, the pointer weight can be reduced further.
A particularly effective configuration of the invention is provided if the pointer flag has a number of portions that can be illuminated independently.
By this means, the different portions of the pointer flag can be emphasized optically and, as a result, the legibility can be improved. For example, the portion adjacent to a scale can have a greater brightness than a portion inclined toward the pointer shaft. At the same time, the portions can also be activated in accordance with the deflection of the pointer flag and, for example when a maximum permissible value is reached, can assume a signal color which stands out optically.
A development of the invention is particularly beneficial in that the pointer flag has a cross section that differs over its length.
By this means, it is possible to implement a large number of stylistic possibilities for improved legibility which are ruled out in the case of pointer flags which can be illuminated conventionally. For example, the pointer flag can have a greater cross section toward the outside or can have abrupt widenings or constrictions. Designs are also conceivable in which the pointer flag is spread at its end inclined toward the scale, and encloses the indicated value between two arms or within a ring on the pointer flag.
A development in which the light source can be used simultaneously to illuminate subareas of a dial is also particularly beneficial.
The reading accuracy may also be improved further by a subarea, for example the surroundings of an indicated value, being additionally illuminated by means of the light source, and the remaining values (as a result of t heir relative darkening) being blanked out at the same time.
It is advantageous if the color of the light source can also be perceived by a viewer even with a high ambient brightness, so that the pointer appears in the same color both during the day and at night, and therefore appears to be easily legible.